1. Technical Field
This invention relates to a driving apparatus of a light emitting diode, and more particularly to a light emitting diode used as a back light of a flat panel display and a liquid crystal display using the same.
2. Description of the Related Art
Currently, a display device plays a very important role and several display devices has been extensively used in various industry fields.
Generally, a display device is a device for transferring various visual information. That is, a display device is an electronic device for converting an electronic information signal that is output from several electronic appliances to an optical information signal and performs a function for visually connecting between a human being and an electronic device.
In the display devices, a display device in which an optical information signal is displayed by a light emitting process is called a light emitting display device and a display device in which an optical information signal is displayed through optical modulation due to a reflection, scattering, interference phenomena, or so on is called a light receiving display device.
The light emitting display device is called an active display device and comprises, for example, a cathode ray tube (CRT), a plasma display panel (PDP), an organic electroluminescent display (OELD).
The light receiving display device is called a passive display device and comprises, for example, a liquid crystal display (LCD) and an electrophoretic image display (EPID).
Recently, due to a rapid progress of semiconductor technology, decreases in voltage and power of several electronic devices and decreases in size, decrease in thickness, and decreases in weight of electronic appliances are required. Accordingly, flat panel displays such as the liquid crystal display, the plasma display panel, and the organic electroluminescent display have been developed and a liquid crystal display that can accommodate the decrease in size, decrease in weight, and decrease in thickness and that has low power consumption and a low driving voltage has been in the spotlight among the flat panel displays.
The liquid crystal display is a display device for displaying a desired image by forming a liquid crystal layer having dielectric anisotropy between an upper substrate and a lower substrate, which are transparent insulating substrates, changing molecule arrangement of a liquid crystal material through adjusting an intensity of an electric field formed in the liquid crystal layer, and thus adjusting an amount of light transmitted in the upper substrate, which is a display plane.
Because the liquid crystal display is a light receiving display device which itself cannot emit light, the liquid crystal display requires a back light that is positioned at the rear of a liquid crystal panel for displaying an image and to uniformly sustain brightness of an entire screen.
As a light source of the back light, a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp (EEFL), or other sources have been used. However, recently, the light emitting diode that can semi-permanently use and have an excellent energy saving effect, compared to the CCFL and the EEFL, has been promoted as a future generation light source.
So far, the light emitting diode has generally been used as a light source of a back light for a small-sized liquid crystal display devices such as mobile phones. However, recently, as the brightness of the light emitting diode improves, the light emitting diode is used as a light source of a back light for medium and large-sized liquid crystal display devices and has been gradually widely used.
Hereinafter, a light emitting diode for a back light of an existing liquid crystal display and a driving circuit thereof will be described.
FIG. 1 is a diagram illustrating a driving circuit of a light emitting diode for a back light of the liquid crystal display in the related art.
To drive a plurality of light emitting diodes D1 to D9 that are connected in series to each other, a driving circuit 1 of the light emitting diode in the related art boosts an input voltage to a predetermined level and outputs the voltage. For example, if an input voltage of 18V to 48V is transferred to the driving circuit 1 of the light emitting diode, the driving circuit 1 of the light emitting diode boosts the input voltage and outputs 200V to 380V as an output voltage according to the number of the light emitting diodes D1 to D9.
However, the driving circuit of the LED for the back light of the liquid crystal display in the related art requires many basic parts in constituting a unit circuit as shown in FIG. 1, whereby a circuit structure is complicated. Particularly, because many light emitting diodes are connected to the unit circuit, it is required to boost an input voltage to a high level of voltage.
Further, because the input voltage should be boosted to a high level of voltage, a separate over voltage protection (OVP) circuit is required to satisfy a safety specification, whereby there may be a problem that energy conversion efficiency is deteriorated.